Brush assembly for an electric motor

ABSTRACT

An electric motor includes a stator, an armature rotatably received within the stator and having an armature shaft on which a commutator is mounted, and a brush assembly defining a first surface facing the stator and a second surface opposite the first surface. The brush assembly includes a brush card mount disposed around the commutator, brushes in sliding contact with the commutator to supply electric current to the commutator, and thermally-conductive brush holders. Each brush holder a base portion disposed substantially along a same plane as a surface of the brush card mount to form the first surface of the brush assembly, and a main portion protruding from the second surface of the brush assembly to house a respective brush. The base portions of the brush holders are exposed on the first surface of the brush assembly to transfer heat generated by the brushes through the first surface of the brush assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This utility application claims the benefit of U.S. ProvisionalApplication No. 61/864,264 filed Aug. 9, 2013, and U.S. ProvisionalApplication No. 61/932,932 filed Jan. 29, 2014, contents of both ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a brush assembly for electric motors,and more particularly to a brush assembly for motors used in electricpower tools.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Known portable power tools typically have an electric motor receivedwithin a tool housing. One common type of electric motor used in powertools has a rotor, a stator, and brushes. The rotor includes a rotorshaft, laminations mounted on the rotor shaft, armature windings woundin slots in the lamination stack, and a commutator mounted on the rotorshaft and electrically connected to the armature windings. The statormay have field windings wound in laminations, or may have permanentmagnets. The brushes are mounted in brush housings, often known as brushboxes or brush holders, in sliding electrical contact with thecommutator. Electric current is supplied from a power source through thebrushes to the commutator, and from the commutator to the armaturewindings.

The brushes and brush holders are typically part of a brushassembly(ies). The brush holders and brushes are disposed diametricallyopposite to each other with the commutator disposed therebetween. Thebrush assembly(ies) includes springs that urge the brushes against thecommutator. Exemplary brush assemblies may utilize two or four brushesaround the commutator.

Generally, in brush assemblies, transmission of electric current acrossthe sliding interface between the brushes and the motor commutatorgenerates a considerable amount of heat. This heat is often associatedwith the material used in the brushes. Such materials have relativelyhigher electrical resistance in order to enhance desirable brushproperties such as low friction coefficient and high durability. Theheat is also generated from the electrical arcing that occurs whenelectrical switching occurs as the commutator and brushes rotate withrespect to each other. It is desirable for this heat to be transferredaway from the brushes and dissipated, for example by impinging air flow.

Conventional brush holder designs often include a brush card mount thatis made of a plastic material and the brush holders mounted on a topsurface of the brush card mount. The plastic brush card mount separatesthe brush holders and the brushes from the rest of the motor, where acooling fan is usually disposed to cool the motor stator and armature.This results in a high thermal coefficient between the brushes and thecooling air, which correspondingly results in high temperatures. Someconventional designs utilize larger brushes or larger air flow paths toincrease the surface area of the brushes or brush holders in the path ofthe airflow, but such designs result in larger and more expensivemotors.

What is needed is a brush assembly design that enables more efficientheat transfer from the brushes and brush holders.

SUMMARY

According to an embodiment of the invention, an electric motor isprovided including: a stator, an armature rotatably received within thestator and having an armature shaft on which a commutator is mounted,and a brush assembly. In an embodiment, the brush assembly defines afirst surface facing the stator and a second surface opposite the firstsurface. In an embodiment, the brush assembly includes a brush cardmount disposed around the commutator, brushes in sliding contact withthe commutator to supply electric current to the commutator, andthermally-conductive brush holders. In an embodiment, each of the brushholders includes a base portion disposed substantially along a sameplane as a surface of the brush card mount to form the first surface ofthe brush assembly, and a main portion protruding from the secondsurface of the brush assembly to house a respective brush. In anembodiment, the base portions of the brush holders are exposed on thefirst surface of the brush assembly to transfer heat generated by thebrushes through the first surface of the brush assembly.

According to an embodiment, a fan is rotatably attached to the armatureand disposed between the brush assembly and the stator. In anembodiment, the first surface of the brush assembly is disposed in closeproximity to the fan. In an embodiment, rotation of the fan causes airto flow from the second surface of the brush assembly, through the brushassembly and around the commutator, towards the fan. In an embodiment,the first surface of the brush assembly forms a baffle for the fan toredirect airflow generated by the fan in a centrifugal direction.

In an embodiment, the brush card mount includes a plurality of openingsand the main portions of the brush holders protrude from the baseportions through the plurality of openings. In an embodiment, the brushholders are received from the first surface of the brush assemblythrough the openings of the brush card mount and are affixed to thebrush card mount on the second surface of the brush assembly. In anembodiment, the brush card mount includes recessed surfaces around theopenings on the first surface of the brush assembly and the baseportions of the brush holders are partially disposed within therespective recessed surfaces. In an embodiment, the base portion isprovided as a separate piece from the main portion.

In an embodiment, the brush card mount includes a plurality of openingsand the brush holders are slidingly received within the openings fromthe periphery of the brush card mount in a radial direction. In anembodiment, the brush card mount includes separate planar piecesseparated by the openings, and the base portions of the brush holdersare slidingly received within the openings and supported by the separateplanar pieces of the brush card mount. In an embodiment, each brushholder includes grooves on both sides thereon and the planar piecesinclude side guides on both sides thereon arranged to mate with thegrooves of the brush holder as the brush holder is received inside theopening of the brush card mount.

In an embodiment, there are four brush holders disposed equidistantlyaround a periphery of the brush card mount. In an embodiment, the brushholders occupy at least 40% of a total area of the first surface of thebrush assembly.

In an embodiment, the brush card mount includes a planar portiondisposed around the commutator, a bridge portion disposed at an end ofthe commutator and extending from the planer portion via two or morelegs, and at least one metal routing(s) disposed on or within the bridgeportion to electrically couple the brushes.

According to an embodiment of the invention, a power tool is provided,comprising a housing and an electric motor disposed in the housing.According to an embodiment, the motor includes a stator, an armaturerotatably received within the stator and having an armature shaft onwhich a commutator is mounted, and a brush assembly. In an embodiment,the brush assembly defines a first surface facing the stator and asecond surface opposite the first surface. In an embodiment, the brushassembly includes a brush card mount disposed around the commutator,brushes in sliding contact with the commutator to supply electriccurrent to the commutator, and thermally-conductive brush holders. In anembodiment, each of the brush holders includes a base portion disposedsubstantially along a same plane as a surface of the brush card mount toform the first surface of the brush assembly, and a main portionprotruding from the second surface of the brush assembly to house arespective brush. In an embodiment, the base portions of the brushholders are exposed on the first surface of the brush assembly totransfer heat generated by the brushes through the first surface of thebrush assembly.

The above-described embodiments substantially improve heat transfer fromthe brushes and brush holders by providing metallic heat sinks on thefirst surface of the brush assembly on the path of air flow from themotor fan. This arrangement thus improves heat transfer from thebrushes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B depict perspective side views of a four-pole brushassembly (also referred to herein as brush card) 100, according to anembodiment;

FIGS. 2 and 3 respectively depict top and bottom views of the four-polebrush card 100, according to an embodiment;

FIG. 4 depicts a perspective expanded view of brush card 100, accordingto an embodiment;

FIG. 5 depicts a zoomed-in view of the bridge portion 112 showing thechannels 124 a and 124 b and the vertical drop 128 within the channel124 b, according to an embodiment;

FIG. 6A depicts a rear perspective view of the brush card mount 102prior to the bearing 136 being inserted and heat-staked, according to anembodiment;

FIG. 6B depicts a rear perspective view of the brush card mount 102after the bearing 136 is inserted into the bearing pocket 126 andheat-staked, according to an embodiment;

FIG. 7A depicts a front perspective view of a four-pole brush card 200,according to an alternative embodiment;

FIG. 7B depicts a rear perspective view of the brush card mount 202 ofthe brush card 200, according to an embodiment;

FIG. 7C depicts a perspective view of the brush card mount 202,according to an embodiment;

FIG. 8 depicts a rear perspective view of a conventional brush assembly300 including a brush card mount 302, brush holders 304, and brushes306, according to an embodiment;

FIGS. 9A-9C depict various expanded and assembled views of a brushholder 104 and a brush card mount 102, according to an embodiment;

FIG. 10 depicts a zoomed-in perspective view of the top surface of thebrush card 100 showing the upwardly-projecting legs 158 crimped over thetop surface of the brush card mount 102 within recessed pockets 172,according to an embodiment;

FIGS. 11A through 11D depict various views of the brush holder 104,including the base piece 150 and the main piece 160 crimped together,according to an embodiment;

FIG. 12 provides a rear perspective view of the brush card 100 and acut-off portion of a motor fan 502, according to an embodiment;

FIG. 13A depicts a perspective view of a brush card 400 having amodified (extruded) brush holder 404 design, according to an alternativeembodiment;

FIG. 13B depicts a perspective view of the brush card 400 without thebrush holders 404, according to an embodiment;

FIGS. 14A and 14B depict perspective and cross-sectional views of thebrush holder 404, according to an embodiment;

FIG. 15 depicts a partial cross-sectional view of a power tool 500including a motor assembly 510 having a brush assembly 100, a stator512, a rotor 514, and a fan 502, according to an embodiment;

FIGS. 16A-16C depict various perspective and side views of the fan 502,according to an embodiment;

FIG. 17 depicts a zoomed-in view of the fan 502 inside the tool housing508, according to an embodiment;

FIG. 18 depicts a cross-sectional view of a tool housing 508 includingthe brush card 100, without the motor 510 and the fan 502, according toan embodiment;

FIG. 19 depicts the fan 502 mounted on a fully wound and molded rotor514, according to an embodiment;

FIG. 20 depicts a perspective view of the same fan 502 and rotor 514without the windings 552, according to an embodiment;

FIGS. 21A-21C depict perspective views of a rotor end insulator 560,according to an embodiment;

FIG. 22 depicts a spring 110 used in the brush card 100, according to anembodiment;

FIG. 23 depicts a partial perspective view of the brush card 100 withthe spring 110 inserted on the post 108 and engaging the brush 106,according to an embodiment;

FIG. 24 depicts a rear view of the brush card 100 showing the first leg604 of the spring 110 inside the pocket 614, according to an embodiment;and

FIG. 25 depicts a brush 106 inside the brush holder 104, according to anembodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to various aspects and embodimentsof the invention, examples of which are illustrated in the accompanyingdrawings.

Four-Pole Brush Card with Bridge Connector

A first aspect of the invention is discussed herein. FIGS. 1A and 1Bdepict perspective side views of a four-pole brush assembly (alsoreferred to herein as brush card) 100, according to an embodiment of theinvention. FIGS. 2 and 3 respectively depict top and bottom views of thefour-pole brush card 100, according to an embodiment. In thisembodiment, brush card 100 includes a brush card mount 102 and fourbrush holders 104. The brush card mount 102 has a substantially circularcircumference and the four brush holders 104 are arranged equidistantlyon four sides of the brush card mount 102. Each brush holder 104accommodates a brush 106 therein. The brushes 106 housed in brushholders 104 facing each other are electrically connected to one another,as discussed below. Both ends of each brush holder 104 are open to allowradial movement of the brush 106 towards and away from a center of thebrush card 100. The brush card mount 102 includes upright posts 108 inclose proximity to the brush holders 104. Each post 108 is arranged tohold a wound portion of a spring 110. Each spring 110 includes anextended arm that engages a back surface of brush 106 inside the brushholder 104 to bias the brush 106 towards the center of the brush card100.

According to an embodiment, brush card mount 102 includes a planarportion, to which brush holders 104 are secured. A middle section of theplanar portion includes an opening that receives a motor commutator (notshown). The brush card mount 102 also includes a bridge portion 112arranged above the commutator opening (and the commutator) and connectedto the planar portion via four bridge legs 114 a, 114 b, 116 a, and 116b. Bridge legs 114 a, 114 b, 116 a, and 116 b extend longitudinally(i.e., in the direction of the motor, at a substantially right anglewith respect to the plane of the brush card mount 102) from the planarportion to the bridge portion 112. Radially formed between bridge legs114 a, 114 b, 116 a, and 116 b are gaps that allow for the radialmovement of brushes 106.

According to an embodiment, bridge leg 114 a and 114 b form walls thatextend radially from the bridge portion 112 to (or near) outer edges ofthe brush card mount 102. In an embodiment, the bridge legs 116 a and116 b similarly extend towards (or near) outer edges of the brush cardmount 102. This arrangement strengthens support for the bridge portion112. In addition, bridge leg 114 a mechanically supports andelectrically isolates two terminals 118 a and 118 b provided on bothsides of its outward-extending wall. Terminals 118 a and 118 b areconnected to metal routings 120 a and 120 b, which extend over thebridge portion 112 to bridge leg 114 b. Metal routings 120 a and 120 bconnect the brushes 106 facing each other to one of the terminals 118 aand 118 b. Specifically, ends of metal routings 120 a and 120 b areconnected via wires 122 to either corresponding brush holders 104 orbrushes 106 via wires 120. In an embodiment, metal routings 120 a, 120 bare routed around a shaft bearing pocket 126, which holds a shaftbearing 136, as discussed below in detail. In an embodiment, metalrouting 120 a crosses over routing 120 b to allow for opposite brushes106/brush holders 104 to be connected to the same terminal 118 a or 118b.

FIG. 4 depicts a perspective expanded view of brush card 100, accordingto an embodiment. In this figure, brush card mount 102 is depictedseparately from the rest of the brush card 100 components. In anembodiment, bridge portion 112 of the brush card mount 102 includeschannels 124 a, 124 b that accommodate metal routings 120 a, 120 b. Eachof the channels 124 a, 124 b in this embodiment extends from leg 114 ato leg 114 b, around shaft bearing pocket 126. Metal routings 120 a, 120b include vertically-extending teethed ends 132 a, 132 b on both ends,arranged to get pushed into slots 134 of bridge legs 114 a, 114 b duringthe assembly process. It is noted that other means such as an adhesiveor molding mean be used to secure the metal routings 120 a, 120 b to thebridge portion 112. Terminals 118 a and 118 b integrally extend from theroutings 120 a and 120 b above the teethed ends 132 a and 132 b on thetwo sides of leg 114 a. Channel 124 b includes a recessed portion 128that penetrates into bridge portion 112 between the shaft bearing pocket126 and the bridge leg 114 b. In an embodiment, recessed portion 128 issubstantially vertical. The channel 124 b extends out through the bridgeportion 112 from the end of the recessed portion 128 along a lowerplane. The recessed portion 128 intersects a portion of channel 124 a.

Metal routing 120 b includes a penetrating portion 130 that is receivedinside the recessed portion 128 of channel 124 b. In an embodiment, thepenetrating portion 130 is substantially vertical. This allows routing120 a to cross over metal routing 120 b as it extends through channel124 a to bridge leg 114 b. This arrangement creates a gap between themetal routings 120 a and 120 b that, in an embodiment, is 1-3 mm. Thisgap is sufficient to prevent an electrical shortage.

FIG. 5 depicts a zoomed-in view of the bridge portion 112 showing thechannels 124 a and 124 b and the recessed portion 128 within the channel124 b, in an embodiment.

Shaft Bearing Retention

Another aspect of the invention is discussed herein with reference toFIGS. 6A-7C.

According to an embodiment, as shown in FIG. 1A through FIG. 3 and FIGS.6A and 6B, motor shaft bearing 136 is secured inside the shaft bearingpocket 126 via heat staking. FIG. 6A depicts a rear perspective view ofthe brush card mount 102 prior to the bearing 136 being inserted andheat-staked. As shown in this figure, the brush card mount 102 includesa plastic ring 138 around the back side of the pocket 126. In anembodiment, plastic ring 138 slightly projects from a rear surface ofthe bridge portion 112. FIG. 6B depicts a rear perspective view of thebrush card mount 102 after the bearing 136 is inserted into the bearingpocket 126 and heat-staked. In this embodiment, after the shaft bearing136 is inserted into the pocket 126, the plastic ring 138 is heated todeform around the circumference of the rear surface of the shaft bearing136. The plastic ring 138 in this manner folds inwardly to contain thebearing 136. This secures the bearing 136 inside the pocket 126.According to an embodiment, the remaining components of the brush card100 are assembled on the brush card mount 102 after the heat-staking iscompleted. Once brush card 100 is fully assembled, the bearing 136 ispress-fitted onto the motor shaft (not shown) during motor assembly.

FIG. 7A depicts a front perspective view of a four-pole brush card 200,according to an alternative embodiment of the invention. FIG. 7B depictsa rear perspective view of the brush card mount 202 of the brush card200, according to an embodiment. FIG. 7C depicts a perspective view ofthe brush card mount 202, according to an embodiment. As shown in thesefigures, the top of the bridge portion 212 does not include an openingas in the previous embodiment. In other words, pocket 226 of the brushcard mount 202 is not open-ended. Instead, pocket 226 encloses the topend of the shaft bearing 236. Metal routings 220 a, 220 b extend inparallel over the bridge portion 212. The pocket 226 includes one ormore pins 228 inserted through two through-holes that extend into thepocket 226 within the bridge portion 212. The through-holes arepositioned to place a portion of the pins 226 inside the pocket 226, asshown in FIG. 7B. The shaft bearing 236 includes a groove 238 formed onits outer surface. The groove 238 has the same width as the pins 226. Asthe shaft bearing 236 is forced inside the pocket 226, it slides pastthe pins 228 until the pins 228 are locked inside the groove 238. In analternative embodiment, the shaft bearing 236 is first placed inside thepocket 226 and the pins 228 are then inserted through the grooves 238.The pins 228 securely hold the shaft bearing 236 inside the pocket 226.

In an alternative embodiment, instead of using two pins 226 as shownherein, any retention mechanism, e.g., an E-clip, a C-clip, a singlepiece U-shaped retainer, a split ring, etc., may be used to retain theshaft bearing 236.

Bottom-Mount Brush Holder

Another aspect of the invention is discussed herein with reference toFIGS. 8-14B. FIG. 8 depicts a rear perspective view of a conventionalbrush assembly 300 including a brush card mount 302, brush holders 304,and brushes 306. Brush holders 304 are mounted on a top surface of thebrush card mount 302. Brush holders 304 include legs 308 that penetratethrough openings, or around the edges of the brush card mount 302 andcrimp on the rear side of the brush card mount 302. Brush holders 304may be provided as single piece or multi-piece units.

In four-pole motor platforms, particularly in the context of power tooldesigns, the brush card 300 is arranged around a motor commutator, withthe rear surface of the brush card 300 facing the motor stator and fan.The top surface of the brush card 300 (i.e., where the brush holders 304are located) is arranged and at end of the power tool in the proximityof air inlets. Brush holders 304 generate a substantial amount of heatresulting from the electrical current passing through the brushes 306.As the fan spins, air is sucked through the air inlets. Air flows aroundthe brush holders 304, through the opening in the brush card 300 andaround the outer circumference of the brush card 300, into the fan.While the air flow cools the brush holders 304 to some degree, thecooling effect of the air flow in this conventional design is notsufficient in many power tool designs, in particular in high powerapplications. What is needed is a more effective cooling mechanism forthe brush assembly.

According to an embodiment of the invention, as shown in FIGS. 9A-9C, anew brush holder/brush card design is provided. In an embodiment, brushcard mount 102 includes four openings 140 for receiving the brushholders 104 through its rear surface. This results in brush holders 104occupying a large portion of the surface area of the rear surface of thebrush card 100 adjacent the motor fan. Thus, in an embodiment, brushholders 104 act as heat sinks to transfer heat away from the brush card100. This design significantly improves heat transfer as compared to theconventional design discussed above.

According to an embodiment, each opening 140 of the brush card mount102, as viewed from the rear surface of the brush holder 104, is definedby two recessed surfaces 142 of the brush card mount 102 on its sidesand a boundary portion 144 of the brush card mount 102 on its radialend. The recessed surfaces 142 each include two slots 146.

As shown in the expanded view of FIG. 9A, the brush holders 104 (onlyone of which is shown herein) each include a base piece 150 and a mainpiece 160, according to an embodiment. The base piece 150 in thisembodiment includes a flat portion 152 and two side portions 156. Flatportion 152 includes two rectangular slots 154. Side portions 156 eachinclude two upwardly-projecting legs 158.

The main piece 160, in an embodiment, includes a brush-holder portion162 that is shaped to contain two side surfaces and a top surface of thebrush 106. Extending from side ends the brush-holder portion 162 are twoflat portions 166 that extend parallel with the rear surface of thebrush card mount 102. The flat portions 166 each include two slots 168that correspond to and receive upwardly-projecting legs 158 of the basepiece 150. In addition, the brush-holder portion 162 includes twodownward protrusions 164 that correspond to and are received insiderectangular slots 154 of the base piece 150. The side surfaces of thebrush-holder portion 162, in an embodiment, include openings 170 that isopen-ended on a distal end of the brush holder 104 and extends radiallyto accommodate the back and forth movement of the spring 110 and thewires 122.

FIGS. 9B and 9C depict steps of assembling the brush holder 104 into thebrush card mount 102, according to an embodiment of the invention. Asshown in FIG. 9B, the main piece 160 of the brush holder 104 is insertedinto the opening 140 of the brush card mount 102. The top surfaces ofthe flat portions 166 mate with the recessed surfaces 142 of the bushcard 102 around the opening 140. The brush holder portion 162 penetratesthrough the opening 140 and projects above the top surface of the brushcard mount 102. Slots 168 of the main piece 160 in this position arealigned with slots 146 of the recessed surfaces 142.

Next, as shown in FIG. 9C, upwardly-projecting legs 158 of the basepiece 150 are inserted through the aligned slots 168 of the main piece160 and slots 146 of the recessed surfaces 142. Downward protrusions 164are received inside the rectangular slots 154 as the base piece 150comes in contact with the main piece 160. Side portions 156 of the basepiece 150 mate with the back surfaces of the flat portions 166 of themain piece 160. Once this step is complete, the upwardly-projecting legs158 are crimped as discussed below. The flat portion 152 of the basepiece 150, together with the brush holder portion 162, form arectangular box for holding the brush 106.

FIG. 10 depicts a zoomed-in perspective view of the top surface of thebrush card 100 showing the upwardly-projecting legs 158 crimped over thetop surface of the brush card mount 102 within recessed pockets 172.Recessed pockets 172 each include two slanted surfaces (see FIG. 4)between the slots 146. Crimped portions of the upwardly-projecting legs158 rest on these slanted surfaces once they are crimped.

It is noted with reference to FIG. 10 that the top surface of theboundary portion 144 of the brush card mount 102 is recessed toaccommodate insertion of the brush 106 inside the brush holder 104 oncethe brush holder 104 assembly is complete. It is further noted thatopenings 170 of the brush holder 104 are arranged to accommodate theback and forth movement of the spring 110 and the wires 122 along withthe brush 106.

FIGS. 11A through 11D depict various views of the brush holder 104,including the base piece 150 and the main piece 160 crimped together.The brush card mount 102 is not shown in these figures. However, asdiscussed above, in the fully-assembled brush card 100, areas of thebrush card mount 102 between recessed surfaces 142 and recessed pockets172 are sandwiched between the crimp portions of the upwardly-projectedlegs 158 and the top surfaces of the flat portions 166 of the brushholders 104.

The brush holder design of the invention discussed herein providesseveral advantages. The two-piece assembly of the brush holders into thebrush card mount is relatively easy. Furthermore, since the brushholders are inserted through a rear surface of the brush card mount, themetallic base pieces 150 of the brush holders 104 are exposed in closeproximity to the motor fan. The brush holders 104 thus act as heat sinkto transfer heat away from the brush holders 104 and brushes 106. Thisarrangement substantially improved overall heat transfer from the brushcard 100.

FIG. 12 provides a rear perspective view of the brush card 100 and acut-off portion of a motor fan 502, according to an embodiment of theinvention. As shown herein, in an embodiment, the brush holders 104occupy at least 40% of the total surface area of the rear surface of thebrush card 100. Preferably, the brush holders 104 take up at least 45%of the total area of the surface area of the rear surface of the brushcard 100. More preferably, the brush holders 104 take up at least 50% ofthe total area of the surface area of the rear surface of the brush card100. Furthermore, in an embodiment of the invention as discussed indetail below, the rear surface of the brush card 100 (including thebrush card mount 102 and brush holders 104) acts as a baffle for the fan502. As the motor fan 502, including the motor blades 504, spins, air issucked through air vents disposed across the top surface of the brushcard 100, through and around the brush card 100, into the fan 605. Theair is then expelled radially between the fan 502 and the brush card 100through air outlets disposed in alignment with the fan 502. Thegenerated air flow thus makes substantial contact with the rear surfaceof the brush holders 104, which act as heat sinks for the respectivebrush holders 104 and brushes 106, allowing them to cool down. Thisdesign substantially improves heat control over the conventional designof FIG. 8 discussed above.

Brush Holder with Extruded Heat Sink

An alternative brush holder design is discussed herein with reference toFIGS. 13A-14B, according to an embodiment of the invention. FIG. 13Adepicts a perspective view of a brush card 400, according to thisembodiment. The brush card 400 includes a brush card mount 402 and brushholders 404. As in the previous embodiment, brush card mount 402 has asubstantially circular periphery and the four brush holders 404 arearranged equidistantly around the periphery of the brush card mount 402.The brush holders 404 facing each other are electrically connected toone another. Each brush holder 404 houses a brush 406 therein. Both endsof each brush holder 404 are open to allow radial movement of the bushtowards a center of the brush card 400. The brush card mount 402includes posts 408 in close proximity to the brush holders 404. Theposts 408 accommodate springs 410, each of which includes an extendedarm that engages a back portion of a corresponding brush 406 to bias thebrush 406 towards the center of the brush card 400. Metal routings 420a, 420 b are disposed on (over or within) bridge portion 412 to connectbrushes 406 that are arranged opposite each other. As in thepreviously-described embodiments, metal routings 420 a, 420 b cross overeach other within bridge portion 412. Terminals 418 a, 418 b aredisposed at the ends of the metal routings 420 a, 420 b. Wires 422 arealso coupled between brushes 406 and the metal routings 420 a, 420 b.

FIG. 13B depicts a perspective view of the brush card 400 without thebrush holders 404. According to an embodiment, similarly to the previousembodiments, bridge portion 412 includes channels 424 a, 424 b formedtherein for placement of metal routings 420 a, 420 b. Unlike theprevious embodiment shown in FIGS. 9A-12, a planar portion of the brushcard mount 402 includes four separate planar pieces 411 connectedtogether via legs 414 of bridge portion 412. In other words, unlike theprevious embodiment where boundary portions 144 of the brush card mount102 define openings 140 for receiving the brush holder 104, the planarpieces 411 in this embodiment are not connected to one another along themain plane of the brush card mount 400. Instead, planar openings 416between the planar pieces 414 receive the brush holders 404 in a radialdirection. Planar pieces 411 include side guides 415 arranged to bereceived in corresponding grooves of the brush holders 404, as discussedbelow.

In an alternative embodiment, planar openings 416 may be open-ended onthe outer end for receiving the brush holders 404, but close ended onthe inner end to mechanically join the planar pieces 411 to one another.In yet another embodiment, planar openings 416 may be open-ended on theinner end for receiving the brush holders 404, but close ended on theouter end to mechanically join the planar pieces 411 to one another.Placing a ring on either the inner or outer circumferences of the planarpieces 411 to connect the planar pieces 411 together provides mechanicalsupport for the brush card 400 and enhances the moldability of theplanar pieces 411 during the manufacturing process.

FIGS. 14A and 14B depict perspective and cross-sectional views of thebrush holder 404, according to an embodiment. Brush holder 404 in thisembodiment includes a main body 450 and a base portion 452 formedtogether integrally as one piece. The main body 450 includes openings470 for facilitating the back and forth movement of the springs 410 andthe wires 422. The main body 450 includes side projections 454, whichtogether with ends of the base portion 454 form grooves 462. Grooves 462receive side guides 415 of the brush card mount 402 as the brush holders404 slides into planar openings 416. In an embodiment, the grooves 462are press-fitted onto the guides 415. In an alternative embodiment, anadhesive is used to secure the guides 415 inside the grooves 462.

According to an embodiment, once the brush holders 404 are fittedbetween the planar pieces 411, a lower surface of the base portion 452acts as a heat sink to carry heat away from the brush card 400,including the brush holder 404 and the brushes 406, similarly to theprevious embodiment. Additionally, in an embodiment, the brush holder404 includes projections 456, 458 projecting from the main body 450. Inan exemplary embodiment shown herein, four side projections 456 and twotop projections 458 are provided. Projections 456 and 458 increase thetotal surface area of the brush holder 404, thereby improving heattransfer away from the brush holder 404.

It must be noted that while projections 456, 458 shown in FIGS. 14A and14B are used with a single-piece brush holder design, the sameprojections may be incorporated into the two-piece design of FIGS. 9A-12to improve heat transfer.

Motor Fan Assembly

Another aspect of the invention is discussed herein with reference toFIGS. 15-17. FIG. 15 depicts a partial cross-sectional view of a powertool 500, according to an embodiment. In this embodiment, one half ofthe power tool housing 508 is shown for illustration purposes, though itis understood that the second half of the power tool housing includesmore or less the same or similar features. The power tool 100 in thisembodiment includes the brush card 100, including the brush card mount102 and the brush holders 104, disposed at one end of the housing. Motor510 in this embodiment includes a motor stator (i.e., can) 512, a rotor514, and a commutator 516 rotatatably coupled to the rotor 514. Thecommutator 516, only a portion of which is visible in this figure, isdisposed inside the brush card 100 between the four brushes 106. The fan502 is also rotatably attached to the rotor 514. The operation of themotor 510 and its components is beyond the scope of this disclosure andis not discussed in further detail, but reference is made to U.S. Pat.No. 7,126,242 issued Oct. 24, 2006, which is incorporated by referencein its entirety, as an example of an electric motor.

FIGS. 16A-16C depict various perspective and side views of the fan 502,according to an embodiment. FIG. 17 depicts a zoomed-in view of the fan502 inside the tool housing 508. As shown in these figures, fan 502includes a plurality of blades 504 arranged between a first inner ring520 and a second outer ring 522. The inner ring 520 is arranged to matewith the rotor 514, while the second ring 522 is disposed in theproximity of the brush card 100, as shown in FIG. 15. Each fan blade 504includes an inner edge 524 that extends from a first end 520 a of theinner ring 520 towards the rear surface of the brush card 100. In anembodiment, the inner edge 524 is inclined towards the armature 516 andthe rotor 514 (i.e., at an angle to the longitudinal axis of the motor510), though the inner edge 524 may be parallel to the tool housing inan alternative embodiment. Each fan blade 504 also includes an outeredge 526 that extends from the outer ring 522 towards the stator 512substantially in parallel with the longitudinal axis of the motor 510. Afirst side edge 528 extends from a second end 520 b of the inner ring520 to the end of the outer edge 526. The first side edge 528, in anembodiment, is arranged at an angle away from the stator 512 in thedirection of the end of the outer edge 526. A second side edge 530extends from the outer ring 522 to the end of the inner edge 524,substantially parallel to the rear surface of the brush card 100. In analternative embodiment, however, the second side edge 530 may beinclined slightly towards the brush card 100 as it meets the inner edge524.

Since the inner edge 524 of the blades covers less air that the outeredge 526 of the blades as the fan 502 spins, inner edge 524 generateslower air velocity near the center of the fan. In order to generateequal air velocity throughout the fan 502, it is desirable for the inneredge 524 to be longer than the outer edge 526. The embodiment of theinvention discussed above ensures that the length inner edge 524 of eachblade 504 is greater than the length of the outer edge 526. According toa further embodiment of the invention, the outer surface of the innerring 522 includes a slanted surface 532 that is arranged at an angleaway from the brush card 100 in the direction of the outer edge 526. Inan embodiment, this slanted surface 532 may be arranged at at least a 45degree angle with respect to the rear surface of the brush card 100.This arrangement helps reduce the length of the outer edge 526 of eachblade 504 even further for more effective air flow generation.

FIG. 18 depicts a cross-sectional view of a tool housing 508 includingthe brush card 100, without the motor 510 and the fan 502. According toan embodiment of the invention, air inlets 542 and 544 are provided inthe rear and center portion of the power tool housing 508. As the fan502 rotates, it generates an air flow from front inlets 542 through themotor 510, in particular in the area between the stator 512 and therotor 514, in an axial direction to cool the motor 510. The air is thenredirected in a radial direction out of the power tool 500 through airvents 540 disposed in the tool housing 508 adjacent the fan 502.Similarly, the fan generates an air flow from rear inlets 544 throughthe brush card 100, particularly around the brush holders 104, andthrough the area between brush holders 104 and the commutator 516, in anaxial direction to cool the brush card 100. This air is also redirectedin a radial direction out of the power tool 500 through the same airvents 540. The rear surface of the brush card 100 (i.e., brush cardmount 102 together with the brush holders 104) forms a baffle to containthe air flow inside the fan 502 and out of the vents 540. Similarly, theend surface 513 of the stator 512 facing the fan 502 forms a secondbaffle for the fan 502. These baffles ensure that the air is propertyredirected through the vents 540.

The angled surface of the first side edge 528 creates a gap between thestator 512 end surface baffle and the fan 502. Similarly, the angledsurface of the outer ring 522 creates a gap between the brush card 100baffle and the fan 502. These gaps may adversely affect air flow throughthe fan 502. In order to prevent such an adverse affect, according to anembodiment of the invention, two ribs 534 and 536 corresponding to theslanted surface 532 of the outer ring 522 and the first side edge 528,respectively, are provided in the tool housing 508. In an embodiment,the first rib 534 includes a sloped surface disposed in close proximityto and in parallel with the slanted surface 532 of the outer ring 522.Similarly, the second rib 536 includes a sloped surface in closeproximity to and in parallel with the first side edge 528 of the fan501. Both ribs 534 and 536 also include surfaces that are in contactwith the rear surface of the brush card 100 (including a portion of thebrush holders 104 and the brush card mount 102) and the end surface 513of the stator 512, respectively. The ribs 534 and 536 are bothring-shaped and extend around the two housing halves to fully close thegaps between the housing 508 and the fan 502 created by the angledsurfaces of the outer ring 522 and the first side edge 528. In thisembodiment, a combination of the rear surface of the brush card 100(including the brush card mount 102 and the brush holders 104), and thesloped surface of the first rib 534, forms the first baffle for the fan502. Similarly, a combination of the end surface 513 of the stator 512and the sloped surface of the second rib 536 forms the second baffle forthe fan 502. Additionally, in an embodiment, the ribs 534 and 536provide alignment features for placement of the brush card 100 and thestator 512 within the power tool housing 508.

Rotor End Insulator

Another aspect of the invention is disclosed herein with reference toFIGS. 19-21C, and with continued reference to FIGS. 16A-16C.

FIG. 19 depicts the fan 502 mounted on a fully wound and molded rotor514. In this figure, the rotor 514 includes a lamination stack 550,windings 552, and end insulators 560. End insulators 560 are disposed atthe ends of the lamination stack 550 prior to the lamination stack 550being wound. End insulators 560 provide insulation between the rotorwindings and the rotor lamination stack 550 and protect the wires frombeing cut during the winding process. FIG. 20 depicts a perspective viewof the same fan 502 and rotor 514 without the windings 552.

According to an embodiment of the invention, in order to property attachthe fan 502 to the rotor 514, the fan 502 is provided with a pluralityof tongues 580, as shown in FIGS. 16A, 16C, 19 and 20. Tongues 580 in anembodiment project in the direction of the rotor 514 from the inner ring520 of the fan 502. In an embodiment, tongues 580 may be 2-6 mm inlength. In an embodiment, tongues 580 may be disposed equidistantlyaround the periphery of the inner ring 510. The number of tongues 580may correspond to the number of slots in the lamination stack 550,although a lesser number of tongues 580 may be provided. According to anembodiment of the invention, end insulator 560 facing the fan 502 isprovided with a plurality of notches 562 arranged to receive the tongues580 of the fan 502, as discussed below in detail.

FIGS. 21A-21C depict perspective views of a rotor end insulator 560,according to an embodiment of the invention. End insulator 560 ispre-molded to include a base portion 564 shaped to match across-sectional profile of the lamination stack 550. The base portion564 includes radially-extending slots 566 formed between teeth 558 ofthe base portion 564. The slots 566 and teeth 568 respectivelycorrespond to the slots and teeth of the lamination stack 550. At theperiphery of the base portion 564, the teeth 568 extend outwardly alongthe circumference of the base portion 564 to partially close the outerend of the slots 566. The slots 566 of the base portion 564 have walls570 projecting perpendicularly to the base portion 564 (in thelongitudinal direction of the motor) on one side. The walls 570 arearranged to form-fittingly protrude into the slots of the laminationstack 550 to insulate the lamination stack teeth. The walls 570 may be,for example, 4 to 12 mm in depth.

The base portion 564 includes a through-hole 572 at its center portionfor accommodating the rotor shaft. On the side of the base portion 564opposite where the walls 570 are arranged, is an annular ring 574 fittedover the rotor shaft.

In an embodiment, two end insulators 560 are form-fittingly mounted onthe ends of the lamination stack 550. In an embodiment, there may be agap of, for example, 2 to 10 mm between the ends of the inner walls 570of the two end insulators 560 within the lamination stack 550 slots. Asthe coils are wound into the lamination stack slots over the endinsulators 560, the thickness of the walls 570 ensures that no contactis made between the coil and the lamination stack 560. Furthermore, theouter surface of the base portion 564 has a slanted profile near theouter ends of the teeth 568 that forces the coils to be packed tightlyinto the lamination stack slots.

According to an embodiment of the invention, as mentioned above, notches562 are arranged at the outer ends of the teeth 568 on the periphery ofthe end insulator 560 to receive the tongues 580 of the fan 502. Thenotches 562 extend longitudinally through the entire length of the teeth568. This arrangement allows the tongues 580 of the fan 502 to makedirect contact with the end of the lamination stack 550. This embodimentreduces the tolerances associated with the motor over a comparabledesign in which the fan 502 is mounted on the end insulator 560.Specifically, since the tongues 580 are mounted directly on thelamination stack 550, calculating the total tolerances for the fan 502needs only take into account the tolerance levels of the fan 502 and thelamination stack 550, and not the tolerance levels of the end insulator560, which is made of plastic and has a relatively large tolerance. Itis noted that tongues 580 may be secured within the notches 562form-fittingly, or via heat-taking, welding, adhesive-bonding, etc.

According to an embodiment of the invention, with reference to FIGS.16A-16C, 19 and 20, the fan 502 may be further provided with one or moreadditional tongues 582 arranged on opposite ends of the inner ring 520.In an embodiment, tongues 582 are longer than tongues 580 and arearranged to be received between two adjacent teeth of the laminationstack 550. Long tongues 582 are provided to ensure that tongues 580 areplaced inside the notches 562, and not between the adjacent teeth of thelamination stack 550, during assembly.

Spring Assembly

Another aspect of the invention is discussed herein with reference toFIGS. 22-24. FIG. 22 depicts a spring 110, according to an embodiment.Spring 110 includes a wound portion 602, a first leg 604, and a secondleg 606 that is longer than the first leg 604 and includes a hook 608 atits distal end.

FIG. 23 depicts a partial perspective view of the brush card 100,according to an embodiment. In this embodiment, the wound portion 602 ofthe spring 110 is arranged around the post 108 of the brush card mount102. The hook 608 of the second leg 606 engages the back of the brush106. The first leg 604 of the spring 110 engages a pocket 614 of thebrush card mount 102. In an embodiment, pockets 614 for each spring 110are formed within end portions of the bridge legs 116 a, 116 b on bothsides (e.g., close to the periphery of the brush card mount 102). Theposition of the first leg 604 within the pocket 614 allows the torsionspring 110 to be loaded as it engages the back of the brush 106.

During the assembly process, in one embodiment, the first leg 604 isplaced within the pocket 614 as the wound portion 602 is pushed down thepost 108. The second leg 606, which at this point rests on top of thebrush holder 104, is then pulled to engage the back of the brush 106 (oran end portion 620 of the brush holder 104). The problem with thisassembly process, however, is that it is difficult to engage and movethe second leg 606 after the wound portion 602 has been pushed down thepost 108. This process is time consuming and burdensome.

According to an embodiment of the invention, in order to ease theassembly process of the springs 110, the end of the bridge legs 116 a,116 b are each provided with an arcuate surface 612, as shown in FIG.23. Arcuate surface 612 is located above the pockets 614. A slopedsurface 610 is provided extending from the top of the bridge leg 116 aor 116 b to the top of the arcuate surface 612. During the assemblyprocess, after the wound portion 602 is placed on the post 108 butbefore it is pushed down, the hook 608 of the second leg 606 of thespring 110 is placed within a recess 622 of the end portion 620 of thebrush holder 104. The first leg 604 at this point is placed on thesloped surface 610 or the arcuate surface 612. As the round portion 602of the spring 110 is pushed down, the hook 608 remains within the recess622. Meanwhile, the end of the first leg 604 slides down the slopedsurface 610 over the arcuate surface 612, and along the arcuate surface612 until it snaps into the pocket 614. As the first leg 604 moves downthe arcuate surface 612 it loads the torsion spring 110, so the spring110 will be loaded even after the first leg 604 snaps into the pocket614.

FIG. 24 depicts a rear view of the brush card 100 showing the first leg604 of the spring 110 inside the pocket 614, according to an embodiment.As seen herein, the pockets 614 for adjacent springs 110 are locatedunder the arcuate surface 612, forming a mushroom-shaped cross-sectionalprofile. The arcuate surface 612 may be shaped as a half-circle abovethe pockets 614, although a cam surface may be utilized to optimize themovement of the first leg 604 into the pocket 614.

Brush Design

Another aspect of the invention is described herein with reference toFIG. 25. In this figure, brush 106 is shown inside the brush holder 104.As discussed above, the hook 608 of the spring 110 engages the recess622 of the end portion 620 of the brush holder during the assemblyprocess. Once the motor is fully assembled and the commutator is placedinside the brush card 100, the hook 608 and the second leg 606 arepulled down to engage the rear surface of the brush 106.

According to an embodiment of the invention, in order to ease theabove-described step, the rear surface of the brush 106 includes twohumped surfaces 624 and 626 and a groove 628 therebetween. The rearsurface of the brush 106 is designed and arranged such that, after themotor is assembled and the commutator is placed inside the brush card100, a portion of the humped surface 624 is aligned with a lower end ofthe recess 622. Specifically, the recess 622 includes a slanted lowerend 622 a which, as viewed from the side, ends in alignment with (orslightly above) the humped surface 624. Using this arrangement, insteadof having to pull the hook 608 out of the recess 622 and push it downinside the groove 628, the second leg 606 of the spring 110 is simplypushed down. As the second leg 606 is pushed down, the hook 608 (or thesecond leg 606) slides down the slanted lower end 622 of the recess,onto and over the humped surface 624, and into the groove 628. Thisdesign substantially eases the assembly process.

In this embodiment, each the humped surfaces 624 may be semi-circularshaped, although a cam surface may be utilized to optimize the movementof the hook 608 over the humped surface 624. It is also noted that twohumped surfaces are shown in this embodiment to ease the assemblyprocess, but the brush 106 may include a single humped surface above thegroove 628.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the scope of the invention.

1. An electric motor comprising: a stator; an armature rotatablyreceived within the stator, the armature having an armature shaft onwhich a commutator is mounted; and a brush assembly defining a firstsurface facing the stator and a second surface opposite the firstsurface, the brush assembly comprising: a brush card mount disposedaround the commutator; a plurality of brushes in sliding contact withthe commutator to supply electric current to the commutator; and aplurality of thermally-conductive brush holders each having a baseportion disposed substantially along a same plane as a surface of thebrush card mount to form the first surface of the brush assembly, and amain portion protruding from the second surface of the brush assembly tohouse a respective brush; wherein the base portions of the brush holdersare exposed on the first surface of the brush assembly to transfer heatgenerated by the brushes through the first surface of the brushassembly.
 2. The electric motor of claim 1, further comprising a fanrotatably attached to the armature and disposed between the brushassembly and the stator.
 3. The electric motor of claim 2, wherein thefirst surface of the brush assembly is disposed in close proximity tothe fan.
 4. The electric motor of claim 3, wherein rotation of the fancauses air to flow from the second surface of the brush assembly,through the brush assembly and around the commutator, towards the fan.5. The electric motor of claim 4, wherein the first surface of the brushassembly forms a baffle for the fan to redirect airflow generated by thefan in a centrifugal direction.
 6. The electric motor of claim 1,wherein the brush card mount includes a plurality of openings and themain portions of the brush holders protrude from the base portionsthrough the plurality of openings.
 7. The electric motor of claim 6,wherein the plurality of brush holders are received from the firstsurface of the brush assembly through the openings of the brush cardmount and are affixed to the brush card mount on the second surface ofthe brush assembly.
 8. The electric motor of claim 7, wherein the brushcard mount includes recessed surfaces around the plurality of openingson the first surface of the brush assembly and the base portions of thebrush holders are partially disposed within the respective recessedsurfaces.
 9. The electric motor of claim 7, wherein the base portion isprovided as a separate piece from the main portion.
 10. The electricmotor of claim 1, wherein the brush card mount includes a plurality ofopenings and the plurality of brush holders are slidingly receivedwithin the plurality of openings from the periphery of the brush cardmount in a radial direction.
 11. The electric motor of claim 10, whereinthe brush card mount comprises separate planar pieces separated by theplurality of openings, and the base portions of the brush holders areslidingly received within the openings and supported by the separateplanar pieces of the brush card mount.
 12. The electric motor of claim10, wherein each brush holder includes grooves on both sides thereon andthe planar pieces comprise side guides on both sides thereon arranged tomate with the grooves of the brush holder as the brush holder isreceived inside the opening of the brush card mount.
 13. The electricmotor of claim 1, wherein the plurality of brush holders comprises fourbrush holders disposed equidistantly around a periphery of the brushcard mount.
 14. The electric motor of claim 1, wherein the plurality ofbrush holders occupy at least 40% of a total area of the first surfaceof the brush assembly.
 15. The electric motor of claim 1, wherein thebrush card mount comprises: a planar portion disposed around thecommutator; a bridge portion disposed at an end of the commutator andextending from the planer portion via a plurality of legs; and at leastone metal routing disposed on or within the bridge portion toelectrically couple the plurality of brushes.
 16. A power toolcomprising: a housing; and an electric motor including a stator; anarmature rotatably received within the stator, the armature having anarmature shaft on which a commutator is mounted; and a brush assemblydefining a first surface facing the stator and a second surface oppositethe first surface, the brush assembly comprising: a brush card mountdisposed around the commutator; a plurality of brushes in slidingcontact with the commutator to supply electric current to thecommutator; and a plurality of thermally-conductive brush holders eachhaving a base portion disposed substantially along a same plane as asurface of the brush card mount to form the first surface of the brushassembly, and a main portion protruding from the second surface of thebrush assembly to house a respective brush; wherein the base portions ofthe brush holders are exposed on the first surface of the brush assemblyto transfer heat generated by the brushes through the first surface ofthe brush assembly.
 17. The power tool of claim 16, further comprising afan rotatably attached to the armature and disposed between the brushassembly and the stator.
 18. The power tool of claim 16, wherein thebrush card mount includes a plurality of openings and the main portionsof the brush holders protrude from the base portions through theplurality of openings.
 19. The power tool of claim 16, wherein the brushcard mount includes a plurality of openings and the plurality of brushholders are slidingly received within the plurality of openings from theperiphery of the brush card mount in a radial direction.
 20. The powertool of claim 16, wherein the plurality of brush holders occupy at least40% of a total area of the first surface of the brush assembly.